1. Field of the Invention
The present invention relates to a device preferably used for pumping oil or other fluid from a drill hole in the ground, the device including a pump with a driving motor under it and connected to the pump, which are lowered into the drill hole.
The pump comprises a hydraulic screw machine including a screw array including a drive screw and at least one running screw co-acting therewith, arranged in a housing with the drive screw connected to a shaft extending outside the housing on the low pressure side of the device, the screws being provided on the low pressure side of the screw array with mutually co-acting balancing pistons adapted for hydraulically balancing the screws against axially acting forces.
2. Description of the Prior Art
In pumping such as crude oil from deep drill holes in the ground it is known to use centrifugal pumps and piston pumps lowered in the holes. The use of such pumps is associated with certain disadvantages, however. The disadvantages limiting the use of centrifugal pumps are that they have long extension in the longitudinal direction of the drill hole, since they must be provided with several stages connected in series for pumping up from great depths, and also that they have relatively poor efficiency when used for high oil viscosities. A disadvantage limiting the use of piston pumps is that they can only be used at relatively small depths since piston stroke will otherwise be unacceptably long.
Attempts have also been made to utilize screw pumps for conveying oil from drill holes, but these attempts have not been very successful, since it has been found to be very difficult to manufacture an effectively functioning pump with a radial inlet and an axial outlet at the end of the pump opposite the inlet, which is a requirement for its use as a drill hole pump.